1. Field of the Invention
The present invention relates to a position detecting apparatus and a method of detecting a position, and more particularly to a position detecting apparatus and a method of detecting a position, which receive electromagnetic waves from plural satellites and calculate a current position of the apparatus using information detected from the received electromagnetic waves.
2. Description of the Related Art
GPS (Global Positioning System) is a system, which receives electromagnetic waves from plural satellites, and calculates the current position using information included in the received electromagnetic waves. The satellites used for the system are not stationary satellites but 32 mobile satellites are used, which orbit the earth at an altitude of 20,000 kilometers and change constantly their relative positions to the earth. To detect the current position, it is necessary to receive GPS signals at least from three satellites among 32 satellites. In practice, GPS signals are received from four satellites to calculate the current position. Each satellite transmits a signal including main frames each having a 30 second period. The main frame consists of five sub-frames each having a 6 second period. Each sub-frame includes data of 30 bits. The first sub-frame among the five sub-frames (first sub-frame to fifth sub-frame) stores a clock correction coefficient and data representing a satellite state, and the second sub-frame and third sub-frame store “Ephemeris” or orbit information. The fourth sub-frame and fifth sub-frame store “Almanac” or general orbit information common to all the 32 satellites. FIG. 14 is a block diagram illustrating a circuit configuration of a conventional position detecting apparatus using a wristwatch. The position detecting apparatus comprises an antenna 11, RF section 12, base band processing section 13, system section 14 and a power source 15.
RF section 12 receives GPS signals from satellites through the antenna 11, and demodulates the received GPS signal, thereby obtaining a base band signal, and supplies the base band signal to the base band processing section 13. The base band processing section 13 comprises CPU 131, “n” units of search engines 132, synchronization detecting section 133. The synchronization detecting section 133 detects synchronizing signals (hereinafter, refer to as “preamble”) of 8 bits each included at the leading portion of each sub-frame, and inputs the starting timings of the sub-frames into CPU 131. CPU 131 starts up the “n” units of search engines 132 based on the preambles detected by the synchronization detecting section 133. Each search engine acquires one sub-frame and stores data of the sub-frame. In the case where GPS signals are received from four satellites and used to detect the current position, data of five continuous sub-frames which are simultaneously transmitted from the four satellites are successively stored in the five search engines, and these 20 pieces of data in total stored in the search engines are used to calculate the current position. The system section 14 comprises, for example, a time counting device, and displays the current position calculated by the base band processing section 13. The power source 15 comprises, for instance, a small sized battery of a coin type (for example, Battery type 2016) and DC/DC converter, and supplies power to RF section 12, the base band processing section 13 and the system section 14.
With respect to technology for using GPS to detect a position, there have been various proposals.
For example, in a GPS navigation apparatus disclosed in Japanese Patent Publication No. Hei3-42793, Ephemeris data is divided into and collected in the unit of sub-frame, and stored in a memory, thereby reducing a time required for collecting data. More specifically, a flag for collecting sub-frames is provided, and the flag is set to “1” every time a sub-frame is collected. Therefore, it is judged based on the flag whether a sub-frame is one which is collected before, and therefore there is no need to collect the same sub-frame repeatedly, resulting in a short time for collecting sub-frames.
A GPS receiving apparatus disclosed in Japanese Patent unexamined Publication No. Hei 11-304899 comprises a detecting section provided with plural channels, message collecting section for collecting navigation information of satellites demodulated by the detecting section, message analyzing section for analyzing the collected massages, positioning section for calculating a position of a receiver from transmission times and distances from satellites, and a timing specifying section for specifying a timing for the message collecting section to scan a navigation message. When messages are collected through one and more channels, the timing specifying section specifies a timing for other channel. GPS navigation apparatus detects fast a preamble pattern or a bit pattern indicating the head portion of a navigation message transmitted from GPS satellite in order to reduce a time required for all the channels to acquire the preamble patterns, and quickly gathers navigation messages to reduce an idle time, during which no positing operation is executed.
A GPS receiving apparatus disclosed in Japanese Patent unexamined Publication No. 2000-292521, plural channels can acquire GPS satellites respectively, and time information is abstracted from satellite data of the acquired satellites. Distances between the current position of the GPS receiving apparatus and GPS satellites are calculated using the time information and a current time counted by the GPS receiving apparatus. Further, detailed orbit information (Ephemeris) is abstracted from satellite data and positions of the satellites are calculated based on the Ephemeris and the current position of GPS receiving apparatus using the calculated distances. In this way, synchronization with satellite data is established quickly, thereby reducing a time left before the positioning operation starts.
In a position detecting apparatus disclosed in Japanese Patent unexamined Publication No. 2003-194910, data of a satellite received by GPS receiver has a hierarchical structure and is structured in a way such that words are subject to a sub-frame, and further the sub-frames are subject to a main frame. A parity bit for word check is included in a word. GPS receiver executes parity check with respect to every word to judge how many words are no good (“NG”) in a sub-frame, and outputs the number of words which are determined as no good “NG”. A judging section judges depending on the number of words determined as “NG” whether data receiving condition is proper or not. When it is determined that data receiving condition is not proper, a control section shuts down the power supply not to acquire data, and turns on the power supply to acquire data after a predetermined time has lapsed. In a poor data receiving condition, it takes a long time to acquire data. Therefore, when the power is supplied to acquire satellite orbit information, much power is consumed, but in the above apparatus, useless power consumption can be avoided.
The position detecting apparatus having GPS receiver is arranged to acquire five sub-frames consisting of the first to fifth sub-frame continuously. Since the five sub-frames have a period of 30 seconds, it is necessary to supply the power constantly for more than 40 seconds with some margin given before and after the sub-frame receiving operation. But in the conventional position detecting apparatus using a wrist watch, shown in FIG. 14, and other hand held position detecting apparatus, when a coin type battery is used to supply power to peripheral circuits, and the power is supplied continuously for more than 40 seconds, the discharging characteristic of the battery can be deteriorate, inviting excessive voltage drop, and as a result, the apparatus may be broken down due to such excessive voltage drop of the battery.
The present invention has been made to solve the problems involved in the conventional apparatuses, and has an object to provide a position detecting apparatus using a coin type battery or other small sized battery. The position detecting apparatus does not consume battery power uselessly, and therefore, may not be broken down due remarkable voltage drop of the battery, thereby receiving GPS signals from satellites without failure to detect the current position.
According to one aspect of the present invention, there is provided a position detecting apparatus for receiving GPS signals transmitted from satellites, and for detecting a position using the received PS signals, GPS signal including main frame data and the main frame data of one cycle further including “m” pieces of sub-frame data consisting of first sub-frame data to m-th sub-frame data transmitted from the satellite in a time series manner, which apparatus comprises a battery for supplying power, a receiving unit for receiving GPS signal in an operation mode and for ceasing receiving GPS signal in an inoperative mode, the receiving unit, when kept in the operation mode, being supplied with power from the battery, and the receiving unit, when kept in the inoperative mode, being supplied with no power from the battery, an operation control unit for switching the receiving unit from the inoperative mode to the operation mode, and for switching the receiving unit from the operation mode to the inoperative mode, a judging unit for judging whether or not all the “m” pieces of sub-frame data have been acquired by the receiving unit, when the receiving unit is switched from the inoperative mode to the operation mode by the operation control unit, a time calculating unit for, when the judging unit determines that all the “m” pieces of sub-frame data have not been acquired, calculating a time at which the receiving unit is to be intermittently switched from the inoperative mode to the operation mode in synchronization with transmission of the sub-frame data which has not been acquired by the receiving unit, and for instructing the operation control unit to control operation of the receiving unit based on the calculated time, and a position calculating unit for, when the judging unit determines that all the “m” pieces of sub-frame data have been acquired, calculating a current position of the apparatus using positional information included in the acquired “m” pieces of sub-frame data.
According to another aspect of the invention, there is provided a method of detecting a position using GPS signals transmitted from satellites, GPS signal including main frame data and main frame data of one cycle further including “m” pieces of sub-frame data consisting of from first sub-frame data to m-th sub-frame data transmitted from the satellite in a time series manner, which method comprises step A of switching a receiving unit from an inoperative mode to an operation mode and switching the receiving unit from the operation mode to the inoperative mode, the receiving unit being arranged to be supplied with power from a battery in the operation mode to receive GPS signal and to be supplied with no power from the battery in the inoperative mode to cease receiving GPS signal, step B of judging whether or not all the “m” pieces of sub-frame data have been acquired by the receiving unit, when the receiving unit is switched from the inoperative mode to the operation mode at step A, and when it is determined at step B that all the “m” pieces of sub-frame data have not been acquired, step C of calculating a time at which the receiving unit is to be intermittently switched from the inoperative mode to the operation mode in synchronization with transmission of the sub-frame data which has not acquired by the receiving unit, and instructing the receiving unit to operate based on the calculated time, and step D of calculating a current position using positional information included in the acquired “m” pieces of sub-frame data, when it is determined at step B that all the “m” pieces of sub-frame data have been acquired.
According to still another aspect of the invention, there is provided a position detecting apparatus which comprises a power source for supplying power from a battery, a receiving unit for receiving GPS signal transmitted from a satellite in an operation mode and ceasing receiving GPS signal transmitted from the satellite in an inoperative mode, the receiving unit being supplied with power from the power source in the operation mode and being supplied with no power from the power source in the inoperative mode, an operation control unit for intermittently switching the receiving unit from the inoperative mode to the operation mode, and a judging unit for acquiring a part of “n” pieces of particular data from GPS signal received by the receiving unit which is switched into the operation mode by the operation control unit, the “n” pieces of particular data consisting of first data to n-th data transmitted from the satellite in a time series manner, and acquiring the remaining pieces of particular data when the receiving unit is switched into the operation mode at other timing, and for judging positional information based on the acquired “n” pieces of particular data.
According to yet another aspect of the invention, there is provided a method of detecting a position which comprises step A of receiving GPS signal transmitted from a satellite in an operation mode and ceasing receiving GPS signal transmitted from the satellite in an inoperative mode, in the operation mode power being supplied from a power source including a battery and in the inoperative mode no power being supplied from the power source, step B of switching intermittently from the inoperative mode to the operation mode, and step C of acquiring a part of “n” pieces of particular data from GPS signal received when the inoperative mode is switched to the operation mode at step B, the “n” pieces of particular data including first data to n-th data transmitted from the satellite in a time series manner, and acquiring the remaining pieces of particular data when the inoperative mode is switched to the operation mode at other timing, and judging positional information based on the acquired “n” pieces of particular data.